1. Field of the invention
The present invention relates to an exposure calculating apparatus for use in, for example, a camera, and more particularly, to an apparatus which calculates an exposure control data so as to expose a main object properly by dividing a photographing image plane into a plurality of regions and measuring the luminance information of respective regions.
2. Description of the related art
An exposure control apparatus is disclosed, for example, in U.S. Pat. No. 4,423,936 according which a photographing image plane is divided into a plurality of regions, a region in which a main object is present (hereinafter referred to as the main zone) is detected from a plurality of the regions, and an exposure control is performed based on the measured brightness or luminance value of the main zone and the measured luminance values of the other regions. According to this apparatus, a light measuring signal such as an infrared light measuring signal is emitted toward a photographing field, and the photographing distances of objects present in three different regions of the photographing field are found, whereby the region in which the nearest object (main object) is present, namely, the main zone is detected. The luminances of the three regions are detected and an exposure control is carried out based on the measured values of light from the main zone and the other regions so as to obtain correct exposure.
Another exposure calculating apparatus is disclosed in Japanese Patent Laid-Open Publication No. 203022/1987. According to this apparatus, the size of the image of a main object is presumed according to the object distance information and the focal length of the photographing lens, and a light measuring range is changed according to the size. According to the apparatus, the size of the image of the main object located in the center of the photographing image plane is presumed based on the object distance information and the information of the focal length of the photographing lens, and the light measuring region is changed according to the size of the image of the main object, whereby light measuring information to properly expose the main object is outputted.
In the exposure calculating apparatus according to U.S. Pat. No. 4,423,936, the position of the main object is considered besides the measured values, but the size of the main object is not considered. Accordingly, the main object cannot always be exposed properly. For example, if the main object is small, a lot of light reflected from objects other than the light reflected from the main object are incident on the region to be measured. Therefore, the luminance of the main object cannot be accurately measured.
In the exposure calculating apparatus according to Japanese Patent Laid-Open Publication No. 203022/1987, it is indispensable that the main object is present in the center of the photographing image plane. Therefore, if the main object is not located in the center of the photographing image plane, it is impossible to properly expose the main object.